By Andreas Rinke

BERLIN (Reuters) - Britain should keep full access to the European Union's internal market after it leaves the bloc, even if it restricts immigration from the EU, a senior German lawmaker told Reuters.

Norbert Roettgen of Chancellor Angela Merkel's Christian Democrats, who chairs the Bundestag foreign affairs committee, is one of five European experts who proposed that post-Brexit Britain join a new "continental partnership".

"It is in the interests of both the EU and Britain to keep the damage as light as possible after Brexit and relations as close as possible," Roettgen told Reuters.

British Prime Minister Theresa May has promised a "unique deal" allowing Britain to secure trade agreements on good terms while limiting immigration. That is a combination repeatedly ruled out by EU leaders, who say free trade is only possible with free movement of people.

But Roettgen sketched out a vision for a Europe of three circles, with the euro zone at the core, then the other EU states, and finally non-EU states belonging to the "continental partnership", which would give them internal market access.

States in this third circle would join EU trade agreements with third-party countries.

As a condition for membership of the partnership, countries would need to accept the free movement of capital, goods and services - but could be exempt from the free movement of people, the fourth of the EU's so-called "four freedoms".

Roettgen said this third circle could be an option not just for Britain, but also for countries like Switzerland and Norway, and even Ukraine and Turkey. That could resolve the issue of Turkey's EU accession ambitions.

"We need a defined framework for the EU neighborhood," he said, adding that he believed the model would be attractive to the British government even if it would still need to contribute to the EU budget.

"The hard Brexiteers will certainly reject this. But I think the majority of British politicians will accept such payments as the price for access to the internal market," Roettgen said.

Punishing Britain for leaving the EU to ward off the threat of other countries leaving the bloc made no sense, he added.

"First of all, there is not one EU country in which serious thought is being given to leaving the EU. And even if that were the case, it would be wrong to build the EU as a house in which one is imprisoned," Roettgen said.

(Writing by Paul Carrel, editing by Larry King)